Читать книгу Dental Neuroimaging - Chia-shu Lin - Страница 33

Neuroimaging in the modern days highlights a non‐invasive procedure. For example, no surgical procedure is required for scanning the brain. However, for a non‐surgical approach, subjects may still be exposed to ionizing radiation. The diverse methods can be broadly categorized according to what brain features to be assessed. Computed tomography (CT) and magnetic resonance imaging (MRI) primarily focus on imaging brain structure. As an application of X‐ray imaging, CT may be the tool that dentists are primarily familiar with. It is advantageous in providing a good contrast on the bone tissue which is particularly useful for surgical procedures of dental treatment. In contrast, the MRI assesses the brain based on the water molecules (or strictly speaking, the hydrogen nuclei of the water molecules) in brain tissue. An MRI scanner detects the electromagnetic signals derived from the change of nuclear spinning of hydrogen nuclei. MRI can ‘map’ brain structure because the physical events can be affected by the density of protons (i.e. the hydrogen nuclei) and the relaxation processes associated with the biochemical features of brain tissue (e.g. containing less or more fat). Therefore, different anatomical features (e.g. fat‐containing neural fibres and water‐containing cerebrospinal fluid [CSF]) can be contrasted in MRI images. This advantage enables MRI the primary tool to investigate the morphology, including the size and shape, of the anatomical structure of the brain (Jenkinson and Chappell 2018). In contrast to the structure‐oriented methods, functional approaches focus on detecting the neurophysiological or brain signals associated with mental functions. The approaches include electroencephalogram (EEG), magnetoencephalography (MEG), positron emission tomography (PET), and functional MRI (fMRI), as discussed below.